Apparatus, process and article for treating an aqueous solution containing a chemical contaminant. The process includes contacting an aqueous solution containing a chemical contaminant with an aggregate composition comprising an insoluble rare earth-containing compound to form a solution depleted of chemical contaminants. The insoluble rare earth-containing compound can include one or more of cerium, lanthanum, or praseodymium. A suitable insoluble cerium-containing compound can be derived from a cerium carbonate, cerium oxalate and/or a cerium salt. The aggregate composition can include more than 10.01% by weight of the insoluble rare earth-containing compound, and in a particular embodiment consists essentially of one or more cerium oxides, and optionally a binder and/or flow aid. Although intended for a variety of fluid treatment applications, such applications specifically include removing or detoxifying chemical contaminants in water.